1. Field of the Invention
The present invention relates to a detecting method and a detecting apparatus for detecting internal resistance of a rechargeable battery to be inspected, particularly, for instance, internal resistance of a rechargeable battery to be inspected in a rechargeable battery pack having a control circuit in which one or more of a switching element for charging which is capable of performing ON-OFF control, a switching element for discharging, and a detecting element for detecting a charge-and-discharge current value are accommodated in a charging-and-discharging path of said rechargeable battery.
The present invention also relates to a rechargeable battery pack having said detecting apparatus provided therein, and an apparatus in which said detecting apparatus is provided.
The present invention includes a program in which said detecting method is incorporated and a medium in which said program is stored.
A rechargeable battery to be inspected which is subjected to the detection of internal resistance thereof in the present invention will be hereinafter referred to as “inspective rechargeable battery”.
2. Related Background Art
In recent years, along with development of semiconductor elements and development of miniature, light-weight and high performance rechargeable battery, mobile instruments such as portable personal computers, video cameras, digital cameras, cellular phones, and personal digital assistants including palmtop PCs have been rapidly progressed.
Separately, in recent years, the global warming of the earth because of the so-called greenhouse effect to an increase in the content of CO2 gas in the air has been predicted. For instance, in thermal electric power plants, thermal energy obtained by burning a fossil fuel is converted into electric energy, and along with burning of such fossil fuel, a large amount of CO2 gas is exhausted in the air. Accordingly, in order to suppress this situation, there is a tendency of prohibiting to newly establish a thermal electric power plant. Under these circumstances, so-called load leveling practice has been proposed in order to effectively utilize electric powers generated by power generators in thermal electric power plants or the like, wherein using a load conditioner having a rechargeable battery installed therein, a surplus power unused in the night is stored in rechargeable battery installed at general houses and the power thus stored is used in the daytime when the demand for power is increased, whereby the power consumption is leveled.
Further, in recent years, electric vehicles having rechargeable battery and which do not exhaust any polluting substances have been proposed. Besides, hybrid powered automobiles in which a combination of a rechargeable battery and an internal combustion engine or a fuel cell is used and the fuel efficiency is heightened while restraining exhaustion of polluting substances have been also proposed. As the rechargeable battery used in these electric vehicles and hybrid powered automobiles, a high performance rechargeable battery having a high energy density is expected to be developed.
Incidentally, in the mobile instrument, the load conditioner in the load leveling, the electric vehicle or the hybrid powered automobile in which the rechargeable battery is used as above described, it is possible to extend the operation time to the maximum by properly controlling the power outputted from the rechargeable battery depending on internal resistance of the battery on the side of the apparatus in which the battery is accommodated, or it is possible to avoid occurrence of sudden stall of the operation by previously knowing the time necessary to exchange the battery based on information relating to the lifetime of the battery, which is acquired from the internal resistance of the battery. Therefore, in order to prevent the operation of the mobile instrument, the load conditioner, the electric vehicle or the hybrid powered automobile from being suddenly stopped, it is very important to be able to precisely detect the internal resistance of the rechargeable battery used therein.
Separately, in the mobile instrument, the load conditioner, the electric vehicle or the hybrid powered automobile, there is often used a rechargeable battery pack having a rechargeable battery therein and which has a control circuit in which one or more of a switching element for charging which is capable of performing ON-OFF control, a switching element for discharging, and a detecting element for detecting a charge-and-discharge current value are accommodated in a charging-and-discharging path of said rechargeable battery. In this case, it is also very important to be able to precisely detect internal resistance-related information of the whole rechargeable battery pack due to abnormality or deterioration of not only the rechargeable battery but also the respective elements in the battery pack.
Japanese Laid-open Patent Publication No. Hei.9(1997)-134742 (hereinafter referred to as document 1) discloses a method wherein for a rechargeable battery, the internal impedance directly before reaching the discharge termination voltage is measured by an impedance-measuring instrument while flowing an alternate current to determine whether or not the rechargeable battery is deteriorated with respect its performance.
However, the method disclosed in document 1 is not practically applicable for the reasons that such impedance-measuring instrument for measuring the impedance is required to have an alternate current-generating circuit and because of this, the apparatus involved unavoidably becomes large-sized, in addition, during when the rechargeable battery is operated, the measurement cannot be performed, and the measured impedance does not always coincide with the internal resistance component R detected as the magnitude of a voltage drop (IR loss) upon the charging-and-discharging operation.
Japanese Laid-open Patent Publication No. 2002-142379 (hereinafter referred to as document 2) discloses a method wherein internal resistance of a rechargeable battery is detected from the magnitude of a voltage drop upon the pulse-charging operation.
However, the method disclosed in document 2 has such problems as will be described in the following. A particular operation which is different from the operation adopted for ordinary charger is required. Although being different depending on the pulse width (the pulse time), in the pulse-charging, in general, a voltage build-up rate from the open-circuit voltage versus the charging current value in the charging region is lower in comparison with that in the case where the charging is being continuously operated and the battery voltage in the pausing region is not decreased until a prescribed open-circuit voltage, where when based on a voltage difference in this case, internal resistance of the rechargeable battery is detected, the value of the detected internal resistance becomes to be smaller than the internal resistance component R detected as the magnitude of a voltage drop (IR loss) upon operating the charging and discharging.
Japanese Laid-open Patent Publication No. Hei.7(1995)-240235 (hereinafter referred to as document 3) discloses a method wherein internal resistance of a rechargeable battery is detected from the magnitude of a voltage drop of the rechargeable battery which is measured by suspending the charging operation.
However, the method disclosed in document 3 has such problems as will be described in the following. A particular operation which is different from the operation adopted for ordinary charger is required, as well as in the case of the method disclosed in document 2. In addition, it is necessary to suspend the charging operation for a long period of time in order to precisely measure the magnitude of the voltage drop of the rechargeable battery, where the time required to full-charge the rechargeable battery is unavoidably elongated, and this invites inconvenience and lowers the working efficiency.
In order to solve such problems as described in the above, Japanese Laid-open Patent Publication No. 2002-50410 (hereinafter referred to as document 4) discloses a method for predictably detecting internal state of an inspective rechargeable battery with respect to electricity storable capacity, internal resistance, and the like from battery voltage of said battery and electric current flown therein by referring to previously acquired data of a normal rechargeable battery which corresponds to said inspective rechargeable battery, with respect to open-circuit voltage thereof which is expressed as function of electricity storable capacity thereof and internal resistance thereof which are expressed by functions of electricity storable capacity, battery temperature and current flow thereof. Although the method disclosed in document 4 is advantageous in that internal state of said inspective rechargeable battery can be predicted at an extremely high precision, there are disadvantages such that basic data of the rechargeable battery under various conditions are necessary to be acquired and a large amount of labor is required for the acquisition such data.